Method of coating wire and apparatus therefor



Jan. 23, 1962 H. B. LlT ETAL 3,018,199

METHOD OF COATING WIRE AND APPARATUS THEREFOR Filed Nov. 22, 1957 llll nAAAA u 27b 27b mun n 25a. 25 iiiffifh 1 Roberf E'- D m n,

United States Patent 3,018,199 METHOD OF COATING WIRE AND APPARATUSTHEREFOR Harry B. Lit, Pittsfield, Mass, and Robert E. Dunton, Canaan,N.Y., assignors to General Electric Company, a corporation of New YorkFiled Nov. 22, 1957, Ser. No. 698,169 17 Claims. (Cl. 117-431) Thepresent invention relates to a method of coating elongated articles suchas wire or the like and is more particularly concerned with an improvedprocess of applying a viscous liquid coating composition on rectangularwire and with apparatus for carrying out such process.

The invention is especially suitable for use in coating rectangularelectrical wire with viscous resin solutions, such as polyvinyl formal,to form an electrically insulating enamel coating thereon.

In providing such insulating coatings on wire, it is standard practiceto apply the resinous coating material in a number of successive stages,such as by passing a Wire a number of times through a bath of thecoating material and baking each coating layer on the wire immedi atelyafter it is applied. The number of passes of the wire through thecontinuous coating apparatus is determined by the desired thickness ofthe final coating deposit. In practice an important factor which governsthe number of passes required to produce a desired coating thickness isthe maximum amount of coating material which can be uniformly depositedin each pass of the wire through the coating apparatus. Attempts todeposit larger amounts than normally applied, using prior processes,have generally resulted in the formation around the wire of anon-uniform film having a so-called dog-bone shape, wherein excessiveamounts of coating material collect on the flat surfaces of the wireadjacent the corners. This effect appears to result from the flow ofmaterial, due to its surface tension, away from the corners of the wireto the flat surfaces. The non-uniform coating consequently produced iswasteful of material and results in wire having a poor space factor.

On the other hand, limiting the amount of material deposited per pass toensure uniformity of layer thickness has made necessary heretofore arelatively large number of passes of the wire through the coatingapparatus to build up the desired over-all thickness of insulatingcoating. As a result, the capacity and productivity of the coatingapparatus and associated baking oven is limited, and the coating processis time consuming and uneconomical.

It is an object of the invention to provide an improved process ofcoating wire or the like having at least one flat side, and particularlyrectangular wire, which avoids the above disadvantages of prior coatingprocesses.

It is another object of the invention to provide a method of coatingrectangular wire and the like wherein a uniform coating of greaterthickness may be deposited with each coating application than heretoforepossible, so that a greater overall build of uniform coating may beobtained with the same number or fewer applications than heretoforerequired.

A further object of the invention is to provide relatively thick enamelcoatings on rectangular wire or the like while avoiding distortedcoatings such as evidenced by the dog-bone effect heretofore produced byknown processes.

It is still another object of the invention to provide a' wire coatingapparatus for effectively carrying out the above improved process.

Other objects and advantages of the invention will become apparent fromthe following description and appended claims.

ice

With the above objects in view, the present invention relates to amethod of coating wire having at least one fiat side, such asrectangular wire and the like, which comprises applying a film ofhardenable liquid coating material on the wire so that the thickness ofthe liquid film on the flat side is substantially greater in the centralportion of said flat side than on the remaining portions thereof, and,after allowing the films of different thick ness to merge into auniformly thick coating, hardening the liquid coating material on thewire.

It will be understood that wire of square cross section may also berectangular wire as the latter expression is used herein.

In a preferred embodiment of apparatus adapted for carrying out theabove method, there is provided in accordance with the invention awire-engaging die member which is particularly constructed for producinga film of differential thickness on each flat side of the wire, thecontact edge face of the die member being preferably formed with acentrally arranged recess means which serves to apply a greaterthickness of liquid coating material to the central portion of the flatwire surface than to the remaining portions thereof.

The invention will be better understood from the following descriptiontaken in conjunction with the accompanying drawing in which:

FIG. 1 is a view of a continuous coating apparatus which may be employedin practicing the present invention;

'FIG. 2 is an enlarged view of a wire coating die device which may beemployed in the apparatus of FIG. 1; and

FIGS. 3, 4, 5 and 6 show various embodiments of die members which may beused in the present invention.

Referring now to the drawing, and particularly to FIG. 1, there is shownan arrangement for continuously coating a moving rectangular wire 1,wherein the wire passes from supply reel 2 through bath 3 of a suitableinsulating coating liquid, such as polyvinyl formal, around a guidesheave 4. Wire 1 having coating material adhering thereto then passesthrough die device 5, which may have a construction as more fullydescribed hereinafter. Die device 5 is carried upwardly by the movingwire until restrained from further upward movement by fixed spacedfingers 6 (see FIG. 2), or other suitable stop means, which permit freelateral and rotational movement of the die device 5 in response to anyswaying or twisting movement of the wire. The wire, with a uniformcoating formed thereon by the die device 5, then continues upwardlythrough a baking or drying oven 7 of any suitable or conventional typewherein the varnish coating applied by the die device 5 to the Wire isheathardened. Thereafter, wire 1 passes around sheave 8 and back to aposition on guide sheave 4 spaced axially from the initial turn of wire.Wire 1 then passes through the coating and drying apparatus in repeatedstages in the manner described until a coating of the desired thicknessis finally built up, it being understood that a die device 5 and stopfingers 6 are provided for each strand of wire passing upwardly in theapparatus. The coated wire is ultimately conducted to a take-up reel 9or other storage means.

FIG. 2 shows the structure of die device 5 in greater detail, and asillustrated therein the die comprises in a preferred embodiment a pairof flat plates 10 and 11 constituting the principal supporting frame ofthe die and having slidably arranged in grooves therein pairs of movablelaminar die members 12, 13, 14 and 15 which yield- :ably engage thesurfaces of the rectangular wire 1 as it passes through the die device.

The die device 5 shown in FIG. 2 is disclosed and claimed in copendiugapplication Serial No. 594,044, Lit and Anderson, filed June 26, 1956,and assigned to the be suitably employed in connection with the presentinvention, it will be understood that other types of die coating devicesmay be used if desired.

In accordance with the invention the die contacting members 12 and 13which respectively engage the fiat sides of the rectangular Wire,whether employed in the device shown in FIG. 2 or other suitable type ofdie device, are provided with a special configuration on their contactedge faces for the purposes of the present invention, as describedhereinafter. The remaining pair of die members 14 and 15 contacting thenarrow edges of the wire may be of conventional construction.

In coating rectangular Wire with insulating enamel in the manner abovedescribed it has been standard practice to use die coating members whichserve to initially apply uniformly thick films of the liquid coatingmaterial on the faces of the wire. Generally, the prior types of diemembers had their contact edges uniformly positioned with respect to theflat sides of the Wire. In some cases, the prior die members hadstraight continuous edge faces for contacting the wire, and in othercases the edge face was provided with serrations forming recesses ofuniform depth. Where either form was used, however, it has been foundthat the finally hardened coating produced on rectangular wire was notuniform, due primarily to the fact that the originally applied liquidmaterial tends to flow away from the corners and collect on the fiatsurfaces of the wire. In particular, attempts to provide thickerindividual layers, such as by using more deeply serrated die members,resulted in the dog-bone type of distorted layer mentioned above. In thefinally built up coating which was thereafter produced by the usualprocess of successive coating applications as above described, suchnonuniformity became magnified, and this resulted in a considerablewaste of material. Further, wound coils and the like formed of such wirewere substantially larger and heavier than was necessary.

In accordance with the invention, it has been found possible tosubstantially increase the thickness of each applied layer while stillmaintaining a uniform thickness in each layer, and thereby provide agreater over-all coating of uniform thickness with fewer applicationsthan previously required, by using die members of the type exemplifiedin FIGS. 3-6 for applying the coating to the relatively wide faces ofrectangular wire. In general, the die members of the present inventionare provided with an edge face recessed in such manner that the openingin the central portion of the edge face has a greater volume than theopening in either of the end portionsof the edge face adjacent thereto,so that for each pass of the wire a greater thickness of liquid, coatingfilm is deposited on the central portion of its flat faces than on theremaining portions adjacent thereto. As a result, it has been found thatthe thus applied liquid film thereafter assumes a uniform thickness, inwhich condition it is hardened by the baking procedure to which it isthen subjected.

FIG. 3 shows a preferred embodiment of a die member which is suitablefor use in carrying out the invention. As shown, die member is providedwith a differentially serrated edge face for making contact with theflat face of the wire 1. It will be understood that in practice two suchdie members would be positioned against the opposite fiat faces ofrectangular wire, in the manner illustrated in FIG. 2. The serrations inthe central portion 214 of edge face 21 are relatively deep as comparedto the serrations on each side 21b thereof, the serrations on theillustrated embodiment gradually decreasing in degree of depth from themaximum in the central portion to the minimum in the outer portions. Ina typical die member used for a rectangular wire of about 300 milswidth, the deepest serrations in the center of the .die member would beabout 22 mils in depth, while the outermost serrations would be about 12mils in depth. It is not necessary to have the contact face serratedfrom one end to the other, but the length of the serrated portion shouldbe sufiicient to extend over the entire Width of the wire face to becoated. Generally, the most satisfactory results have been obtained inso proportioning the serrations in contact with the wire that thecentrally located, relatively deep serrations 21a occupy abouttwo-thirds of the Width of the wire while the outer relatively shallowserrations 21b occupy about one-sixth of the Wire width on oppositesides of the central portion, the shallow serrations preferably beingabout one-half the depth of the central serrations.

FIG. 4 shows another embodiment of the present die member, and in thisform die member 22 has an edge face 23 formed of a non-serrated,rectangular recess 23a flanked by serrated end portions 23b. Asindicated in the figure, the depth of the end serrations 23b may be asgreat as (or even greater than) that of recess 23a and still apply aliquid coating film thinner than that of the central recess. This isreadily apparent in view of the substantially smaller volume of liquidpassing through the serrated portions as compared to that flowingthrough the central recess. As a rule, where serrations similar to thoseshown are employed, the amount of liquid passing through the serratedportion will be about half that passing through the rectangular recesswhen the recess and serrations are of equal depth and extent.

FIG. 5 shows still another embodiment, wherein the edge face 25 ofmember 24 is formed of a concave cen tral recess 25a and serrated endportions 25!). Here also the depth of the end serrations 25b may be asgreat as the deepest portion of recess 25a while still providingsubstantially thinner applied films adjacent the edges of the wire thanin the intermediate portion thereof.

FIG. 6 illustrates still a further modification, wherein die member 26has an edge face 27 formed with a serrated central portion 27a arrangedbetween recessed nonserrated end portions 27 b, the projectingserrations riding on the wire to properly position the die member 26relative to the wire face. In a typical arrangement of this embodiment,the recessed fiat portions 271) may be offset 5 to 6 mils behind theplane of the serration points, the depth of the serrations being about24 mils.

It will be understood that the specific depth and arrangement of theserrations and recesses of the die members employed in particular casesmay vary depending on such factors as the nature and viscosity of thecoating liquid, the width of the wire, the form of the serrations, andother conditions. Further, the die members may have a shape andthickness different from that shown, and still provide the desiredresults.

The following are illustrative examples of procedures which may becarried out in practicing the invention, it being understood that it isnot intended thereby to limit the scope of the invention in any way:

Example I Rectangular copper wire 250 mils in width and 60 mils thickwas coated with polyvinyl formal having a viscosity of 5500 centipoises.A pair of die members were used on the opposite wide faces of the wire,each die member having a form similar to that shown in FIG. 3 whereinthe central serrated portion had relatively deep grooves with a maximumdepth of 21 mils extending over a length of mils and tapering in depthto end serrations about 12 mils deep extending over about 35 milsonopposite sides of the central portion. A final coating was produced ineight passes of the wire through the coating apparatus which wasuniformly 4 mils thick around the wire.

Previous experience using prior art types of die members under similarcoating conditions showed that the same number of passes of the wireproduced a uniform coating only 2 /2 mils thick.

Example II In a procedure using coating material similar to that inExample I, a rectangular wire 500 x 112 mils was provided with a coatingemploying thirteen passes of the wire through the coating apparatus. Thedie members in this process had a central serrated portion of maximumdepth of 22 mils extending about 350 mils in length tapering to endserrations each covering about 75 mils in length and being about 12 milsin depth. A uniformly thick coating of 6 mils around the wire wasproduced by this procedure.

It does not appear necessary in the present invention to critically timethe hardening step after the film applying step in order to provide ahardened film of uniform thickness. tions of the film left by thedescribed die device merge together to a uniform thickness almostimmediately after the wire passes through the die device and remains inthat condition until hardened by the heat of the oven through which thewire then passes. While the exact fiow behavior of the liquid filmapplied by the described arrangement is not fully known, it appearslikely that the initially applied thin portions of the film provided bythe invention are augmented by the flow of excess coating liquiddeposited along the corners of the wire to the adjacent flat surfaces,as well as by the flow of the thicker film at the central portions ofthe flat sides, with the net effect of avoiding the dog-bone depositotherwise encountered and providing an even distribution of insulatingenamel about the wire.

By virtue of the invention as thus described there is provided a wirecoating process and apparatus therefor which produces on rectangularwire relatively thick enamel coatings of uniform depth around the wire,and which enables a reduction in the number of applications heretoforenecessary to produce an over-all uniform build of any given thickness.As a result, the present types of continuous coating apparatus may bemore economically operated and increased in capacity, waste of coatingmaterial is avoided, the coating process requires less time and the wireis subjected to fewer handling and flexing operations encountered in thecoating procedure which tend to make the wire Work-hardened and lessflexible.

While the present invention has been described with reference toparticular embodiments thereof, it will be understood that numerousmodifications may be made by those skilled in the art without actuallydeparting from the scope of the invention. Therefore, the appendedclaims are intended to cover all such equivalent variations as comewithin the true spirit and scope of the invention.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

l. The method of coating wire or the like having at least one flat sidewhich comprises applying -a film of hardenable liquid coating materialon the wire so that the thickness of the liquid film on the fiat side issubstantially greater in the central portion thereof than on theremaining portions thereof, and hardening the liquid coating material onthe wire after the thus applied liquid film merges to a uniformthickness around the wire.

2. The method of coating wire or the like having at least one fiat sidewhich comprises the steps of applying a film of hardenable liquidcoating material on the wire so that the thickness of the liquid film onthe flat side is substantially greater in the central portion thereofthan on the remaining portions thereof, hardening the liquid coatingmaterial after the thus applied liquid film merges to a uniformthickness around the wire, and repeating said steps until a coating ofpredetermined thickness is produced on the wire.

3. The method of coating rectangular wire or the like having oppositeflat sides which comprises applying a film of hardenable liquid coatingmaterial on the wire so that the thickness of the liquid film on eachfiat side is sub- It appears that the thicker and thinner porstantiallygreater in the central portions thereof than on the remaining portions,and hardening the 'liquid coating material after the thus applied liquidfilm merges to a unifor-m thickness around the wire.

4. The method of coating rectangular wire or the like having oppositeflat sides which comprises the steps of applying a film of hardenableliquid coating material on the wire so that the thickness of the liquidfilm on each of the flat sides is substantially greater in the centralportion thereof than on the remaining portions thereof, hardening theliquid coating material after the thus applied liquid film merges to auniform thickness around the wire, and repeating said steps until acoating of predetermined thickness is produced on the wire.

5. The method of providing a uniformly thick coating on a rectangularwire or the like having opposite flat sides, which comprises the stepsof applying a thick film of hardenable liquid coating material on thewire, removing excess coating material from said wire while leaving afilm of liquid coating material thereon which is thicker on the centralportion of each flat side constituting about /3 the width thereof thanon the remaining portions thereof, and hardening the thus applied liquidcoating material after said liquid film merges to a uniform thicknessaround the wire.

6. In an apparatus for providing a coating on wire and the like havingat least one flat side, said apparatus including means for applyinghardenable liquid coating material on the wire, and means for hardeningthe liquid coating material on the Wire, the improvement which comprisesdie means for removing excess liquid coating material deposited on thewire by the applying means while providing a thicker liquid coating onthe central portion of the flat side than on the remaining portionsthereof, said die means comprising a die member having a wire engagingface adapted to contact said flat side of the wire and formed in thecentral portion thereof with a first recessed area and in the remainingportions thereof with second and third recessed areas, the volume of theopening in said first recessed area being greater than the volume of theopening in either of the second and third recessed areas.

7. In an apparatus for providing a coating on wire and the like havingat least one flat side, said apparatus including means for applyinghardenable liquid coating material on the wire and means for hardeningthe liquid coating material on the wire, the improvement which comprisesdie means for removing excess liquid coating mate rial deposited on thewire by the applying means while providing a thicker liquid coating onthe central portion of the flat side than on the remaining portionsthereof, said die means comprising a die member having a wire engagingface adapted to contact said flat side of the wire, said wire engagingface being formed with serrations extending therealong, said serrationsbeing deeper in the central portion thereof than in the remainingportions, the volume of the opening in the serrated central portionbeing greater than the volume of the opening in either of the remainingserrated portions.

8. In an apparatus for providing a coating on wire and the like havingat least one flat side, said apparatus including means for applyinghardenable liquid coating material on the wire and means for hardeningthe liquid coating material on the wire, the improvement which comprisesdie means for removing excess liquid coating material deposited on thewire by the applying means while providing a thicker liquid coating onthe central portion of the fiat side than on the remaining portionsthereof, said die means comprising a die member having a wire engagingface adapted to contact said flat side of the wire, said wire engagingface being formed with a continuous recess extending along the centralportion thereof and with serrations in the remaining portions, thevolume of the opening in said continuous recess being 7 greater than thevolume of the opening in either of the remaining serrated portions.

9. The arrangement as defined in claim 8, wherein said recess of saiddie member is rectangular.

10. The arrangement as defined in claim 8, wherein said recess of saiddie member is concave.

11. In an apparatus for providing a coating on wire and the like havingat least one flat side, said apparatus including means for applyinghardenable liquid coating material on the Wire and means for hardeningthe liquid coating material on the wire, the improvement which comprisesdie means for removing excess liquid coating material deposited on thewire by the applying means while providing a thicker liquid coating onthe central portion of the flat side than on the remaining portionsthereof, said die means comprising a die member having a wire engagingface adapted to contact said flat side of the wire, said wire engagingface being formed with serrations in the central portion thereof andwith a recess, on opposite sides of said central portion, the volume ofthe opening in said central serrated portion being greater than theopening in either of the recessed portions.

12. A die device for use in apparatus for coating wire having a flatside, comprising a member having a wire engaging face formed in thecentral portion thereof with a first recessed area and the remainingportions thereof with second and third recessed areas, the volume of theopening in said first recessed area being greater than the opening ineither of the second and third recessed areas.

13. A die device for use in apparatus for applying a hardenable liquidcoating material on the wire, comprising a member having a wire engagingface formed with serrations extending therealong, said serrations beingdeeper in the central portion thereof than in the remaining portions,the volume of the opening in the serrated central portion being greaterthan the volume oi the opening in either of the remaining serratedportions.

14. A die device for use in apparatus for coating wire having a flatside with hardenable liquid coating material, comprising a member havinga wire engaging face formed with a continuous recess extending along thecentral portion thereof and with serrations in the remaining portions,the volume of the opening in said continuous re- 0655 bcinggrea'ter thanthe volume of the opening in either of the'reniaining serrated portions.

15. A die device as defined in claim 14, wherein said recess isrectangular.

16. A die device as defined in claim 14 wherein said recess is concave.

17; A die device for use in apparatus for coating wire having a flatside with hardenable liquid coating material comprising a member havinga wire engaging face formed with serrations in the central portionthereof and with a recess on opposite sides of said central portions,the

volume of the opening in said central serrated portion being greaterthan the opening in either of the recessed portions.

References Cited in the file of this patent UNITED V STATES PATENTS2,287,589 Wilson et a1 June 23, 1942 2,345,390 Flynn Mar. 28, 19442,346,697 Mungall Apr. 18, 1944 2,433,642 Bailey Dec. 30, 1947 2,447,521Miller et a1. Aug. 24, 1948 2,812,741 OConnor Nov. 12, 1957 2,875,725Lit et a1. Mar. 3, 1959

1. THE METHOD OF COATING WIRE OR THE LIKE HAVING AT LEAST ONE FLAT SIDEWHICH COMPRISES APPLYING A FILM OF HARDENABLE LIQUID COATING MATERIAL ONTHE WIRE SO THAT THE THICKNESS OF THE LIQUID FILM ON THE FLAT SIDE ISSUBSTANTIALLY GREATER IN THE CENTRAL PORTION THEREOF, THAN ON THEREMAINING PORTIONS THEREOF, AND HARDENING THE LIQUID COATING MATERIAL ONTHE WIRE AFTER THE THUS APPLIED LIQUID FILM MERGES TO A UNIFORMTHICKNESS AROUND THE WIRE.